This project has as its main goal a multidisciplinary study of long-term aspects of the relationship between population and the environment in the Great Plains of the United States. This region is important because the grasslands of the Great Plains cover a large part of the United States, and are subject to considerable environmental change. This research involves an examination of the demographic experience of the region and of changes in the environment. The theoretical basis of the project draws on many sources, and is directed toward a model of recursive change in population and environment, one in which changes in one of these factors in one time period influence the other in a subsequent time period, and so on. The project will also examine hypotheses that see land use change as a process of spatial or of cultural diffusion. This project will collect and analyze county-level data about land use decisions and their consequences for the population and the environment over more than a century in order to understand long-term, interactive, and recursive relationships. Researchers will measure the environment impact of population change through soil content and chemistry, and to a lesser extent through species diversity. They will measure the demographic impact of the environmental change through a variety of measures, including population density, migration, social, occupational, ethnic, age and sex structures, and the dynamics of families. This analysis will make use of statistical procedures that take into account spatial and temporal effects. The study will validate its findings and develop new hypotheses with in- depth research about a small sample of communities within the Great Plains. This research will involve a variety of methodologies: detailed analysis of manuscript censuses, tax records, and newspapers; interviews with farm families; and analysis of aerial photographs. The final stage of the project will be to follow these analyses with a model-building and simulation exercise that will first build long-term models of environmental change using the CENTURY soil model system. Then, the investigators will integrate the analysis of demographic and environmental change by building a demographic and social change component to add to the CENTURY model, and comparing the results of the modeling exercise with the historical record for the Great Plains.